Answer:
Cylinder. The explanation is not very exact, more intuition and whatnot, so let me know if there was anything you did not understand.
Step-by-step explanation:
This is assuming the rectangle has its sides parallel with the x and y axes.
Let's try to eliminate them one by one. A cone does not seem likely since it has slanted sides, and spinning the two straight sides will keep the sides straight. This can be used for the pyramid as well. Let me know if this doesn't make sense though.
Now for me I would imagine that rectangle being a sheet of paper, or metal. if you set that sheet atop some dirt or something and then rotated it, what shape would be drawn into the material? It would be a circle. So we know the 3d shapewill have a base of a circle, which leaves us with a cylinder. Again, let me know if this method did not make sense.
